Method of making smooth surface castings of foam metal



1957 J. A. BJORKSTEN METHOD OF MAKING SMOOTH SURFACE CASTINGS OF FOAM METAL Original Filed May 8, 1961 2 Sheets-Sheet 1 FIG. I

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FIG. 2

INVENTOR. BJORKSTEN JOHAN Feb. 28, 1967 BJORKSTEN 3,305,902

METHOD OF MAKING SMOOTH SURFACE CASTINGS OF FOAM METAL Original Filed May 8, 1961 2 sheets sheet 2 39 36 FIG. 4

INVENTOR. JOHAN A. BJORKSTEN ATTORNEY United States Patent Ser. No. 502,767

6 Claims. (Cl. 22-215) This application is a continuation of Serial No. 442,222, filed February 11, 1965, now abandoned, which was a continuation of Serial No. 139,022, filed May 8, 1961, now abandoned, all having the same entitlement.

The present invention relates, in general, to a method of casting foam metal so as to provide a light weight metal panel having an oven, smooth, non-foamed surface with a uniform foamed interior and more particularly to a method of casting foam metal upon a surface of a liquid supporting medium, said liquid being non-reactive with the metal. Foamed metal panels produced by the method of this invention have a smooth even gloss upon the surfaces of the panels which contact the liquid supporting medium during casting.

The term metal foam or foam metal as used herein denotes a manufactured material comprising solid state metal in which discrete cells of vapor or gas having a maximum dimension of between .002 to 1 inch are entrained in substantially uniform dispersion throughout the metal mass. Metal foam is more fully described in US. Patent 2,75 1,289, Method of Producing Metal Foam, John C. Elliott, June 19, 1956, and in US. Patent 2,434,775, Method for Making Foamlike Mass of Metal, Benjamin Sosnick, January 20, 1948.

Metal foam may be produced by introducing gas or finely divided thermally decomposable or volatile fluid or solid material into molten metal in sufficient amounts so as to produce enough gas to exceed the amount of gas necessary to saturate the molten metal. Gas or vapor evolved by the volatilization or decomposition of the volatile or decomposable material causes expansion of the molten metal, and providing metal foam in which cells of gas or vapor having a maximum dimension between .002 and 1 inch or entrained. In producing metal foam it is essential that the molten foam be quickly cooled so as to entrain the gas that is not dissolved in the molten metal in the form of closed cells within the metal.

It is an object of this invention to provide a new and novel method of casting metal foam.

It is another object of this invention to provide a method of casting foam metal upon a surface of a liquid supporting medium.

It is another object of this invention to provide a method of producing a foam metal panel having an especially smooth unfoa-med metal.

Other objects will become apparent from the drawings and from the following detailed description in which it is intended to illustrate the applicability of the invention without thereby limiting its scope to less than that of all equivalents which will be apparent to one skilled in the art. In the drawings like reference numerals refer to like parts and:

FIGURE 1 is a sectional diagrammatic view of a mold according to one embodiment of the invention;

FIGURE 2 is a cross-sectional view of an article produced by the mold of FIGURE 1;

FIGURE 3 is a sectional diagrammatic view of a mold according to another embodiment of the invention;

FIGURE 4 is a sectional diagrammatic view of a mold according to another embodiment of the invention.

My invention is predicated on the discovery that when Patented Feb. 28, 1967 "ice a molten foamable metal mixture is poured and allowed to foam upon a liquid surface, the regions of the molten foamable mixture in contact with a liquid medium having a higher specific gravity than the molten foamable mixture, while foaming will develop a continuous, non-por ous, non-foamed metal skin characterized by extreme evenness and smoothness. The inside portions of the foamable molten mixture that do not contact the supporting liquid medium while foaming will develop a uni form and even cellular structure, while the outside por tions which do not contact the liquid pool tend to develop a non-uniform rough uneven non-porous skin Hence, the foamed structure formed by the method 01 this invention will have a uniform specific gravity anc contain a multiplicity of gas-filled cells; all the cells ma be approximately the same size. A variety of means ma be employed to effect foaming of a molten metal Whil said metal is in contact with a liquid supporting mediun whereby various solid foam objects may be provided Utilizing, for example, a mold having its bottom portior filled with said liquid wherein foaming of the metal take: place, will provide the desired foaming effect of thi: invention. Other apparatus may be utilized to product the desired foamed object of this invention.

The even, smooth, non-foamed outer surface of tilt foamed metal article produced by the method of this in vention is a considerable improvement over the non foamed surface produced by contacting a foamable molter mixture with the cool side walls of a mold during foam ing. The surface produced by the latter method ma be uneven, rough non-porous metal skin with mam grooves and pits while the foamable mixture which con tacts the liquid supporting medium of our invention ha: a smooth, even non-porous metal skin.

The phenomena whereby such a uniform density, even thin, smooth, glossy skin covered metal foam panel i: produced is not completely understood; however, it i: believed that the effects noted are, in general, attributablt to various physical changes that take place within thr molten metal body as it foams on top of the liquid sup porting medium within a mold or any other type of cast ing device. Such changes may be due to the rapid ant even heat transfer in and out of the mold and the uni form heat distribution surface, all provided by the con tacting liquid within the mold. The liquid may alst regulate by means of its heat transfer properties tht amount of heat lost by the material during foaming St as not to dissipate the foam before the molten fOflIIlCt metal cools. This supporting pool of contacting liquir may also prevent one or more grain, micellular or lamina re-orientation, displacement or distortion effects withi1 the molten metal from taking place as it undergoes foam ing. The even heat transfer properties of the liquid sup porting medium are, in general, responsible for the forma tion of a thin, smooth even skin in the outside portion of the molten foamable mixture which contact the liquit supporting medium while foaming as contrasted to tilt nonuniform, uneven, rough skin formed at the outsidt portion of the metal foam which does not contact tl'lt liquid pool during foaming. For the purpose of pro ducing panels, beams, or other construction material con stituting preferred applications of my invention, tht smooth skin surface of the foam metal plates may forn the outside surface of the panel or beam while the un even skin portion may form the inside surface and ma: be joined to another plate at the uneven skin portions It is also possible, by means of this invention, to con struct a mold or casting apparatus whereby all oute portions of the foamed metal product will contact a liquit pool during foaming so as to produce a foam metal pane having a uniform smooth skin on all of its outer sur faces. By the use of this process, foam metal plate taving a specific gravity of less than 1 may be produced. Ience'by the method of this invention it is possible to ast a metal foam panel having a specific gravity as low s .2 or lower.

To the accomplishment of the foregoing and related nds, this method of foaming metal may be performed y utilizing any of the conventional casting apparatus. IGURES 1-4 are indicative of a few of the various lays in which the principle of foaming metal while in ontact with a liquid supporting medium may be perormed.

In describing one embodiment of process of this inention, I refer to FIGURE 1, which is a diagrammatic .lustration of a panel being cast from foamed metal. letal may be melted in tiltable furnace 2, then supplied y pouring over weir spout 3 to mixing vessel 4, where is intermixed by impeller 5 attached to a rotatable haft 5' driven by motor 6, with the foaming agent 7 J form a foamable metal mixture. The foaming agent my be supplied to the mixing vessel as a rod or as a owder contained within a tube by means of a controlling nd feeding device 8. From the mixing vessel 4, the iixture of foamable material may be caused to move 1" may be moved, before it has time to develop any apreciable amount of foam, over the lip 9 into the cavity 0 of mold 11. The bottom portion of the mold 11 is overed with a liquid 12, said liquid having a lower meltig temperature than the metal which is to be foamed ud having a higher specific gravity than foamable metal tixture. The molten metal is then allowed to foam 'hile it contacts the surface of the liquid supporting iedium 12. The foaming is produced by the decomosition or volatilization of the foaming agent.

The mold 11 and the liquid 12 may be maintained at 1e molten temperature of the metal or may be heated to temperature lower than the molten temperature of the ietal being foamed, before the molten foamable metal poured in. However, the temperature of the mold lOllld be at least as high as the melting temperature f the substance used to provide the liquid 11 upon which re molten metal is poured. The mold 11 and liquid 2 may be maintained at the preferred temperature either y virtue of the balanced thermal conductivity properties f the mold material, or by an external heating means hich for simplicity is not shown. The mold may also e maintained at a few atmospheres of pressure by seallg the mold from the atmosphere by means of a tight over or by placing the mold within a sealed pressure essel (not shown) to prevent the foaming agent from olatilizing or decomposing, so as to foam the metal, ntil the foamable material is evenly distributed over the lrface of the molten liquid. After the molten foamble mixture is evenly distributed over the surface of the IOld, the pressure may be released and foaming may Jrnmence.

FIGURE 2 shows the structure of a metal panel prouced by the method of FIGURE 1. Along the bottom irface of the metal panel 17, zone 13 may be provided, rid zone being characterized by the absence of bubbles r foam. This zone 13 is an even, firm, substantially nooth, non-porous metal skin. The thickness of this in may be varied within considerable limits depending u the conditions of operation, but generally the thickess may be between .4 and millimeters. At the top nd side surfaces of the metal panel there is provided zone 16 of an uneven, rough non-pourous metal skin. 1st inside zones 13 and 16, a layer 14 of relatively nall and dense bubbles may be provided. At the cenr or core of the article 17 may be found a layer 15 Jnsisting of large bubbles and having a very low density, rid layer 15 occupying the largest cross-sectional area f the four zones. The cell or bubble size, in general, lay range from .002 to 1 inch in diameter with a mairity of cells in the size range of .01 to 1 inch in dirneter depending upon the particular metal that is foamed and upon the particular foaming agent that may be used to produce this foam. The cells or bubbles within a zone of a given foamed article produced by this new and novel method may have substantially uniform cell sizes. In each of the foamed articles produced by this invention, the outer skins 13 and 16 may be formed so as to change to cellular core 15 in a gradual fashion, with an intermediate partly foamed zone 14 between them, so that both are integral parts of the same continuous phase and no vsharp joints or boundary lines may exist Within the structure. This feature contributes to the strength of this article. The cellular product so-obtained has a lower density than that of the metal of which it is formed, the reduction in density depending upon the nature of the foaming agent used, the metal used for foaming and the operating conditions for producing the foam.

Another embodiment of the invention is shown in FIGURE 3. In this embodiment, the furnace. or metal storage tank 20 may be maintained under a pressure high enough to substantially repress the cell-forming reaction in the metal composition. Agitation may be provided by mechanical or electromotive agitation means 21. The tank may be connected to the mold 22 by means of the closeable inlet 23. The bottom of the mold 22 is filled with a liquid 25 having a low'er melting temperature and a higher specific gravity than the foamable metal mixture. The foaming agent and metal to be foamed may be first placed in the furnace 2b which may be then pressurized withgas introduced at 24 and the components may be then agitated for good dispersion, under pressure, so that foaming does not take place at that point. The mixture may be next fed by injection into the mold 22 while the mixture is under pressure, or as an alternative, so rapidly that only a very slight degree of foaming has had time to take place before the mixture is introduced into the mold. After the foamable mixture has been completely poured into the mold, the pressure may be fully released in the mold and the metal allowed to foam while in contact with the liquid 25. The portion of the metal in contact with the liquid pool 25 forms a thin non-porous skin. The liquid pool 25 conducts heat evenly out of the foamable mixture as it undergoes foaming and into the air so that an even and uniform foamed structure may be formed in regions not in contact with the liquid pool 25.

Another embodiment of this invention is shown in FIG- URE 4. In this case a mold 30 is used which may contain two halves 31 and 32 which may be pivotally connected at 33. Mold half 31 may be equipped with a liquid supporting medium 34 and an agitator 35, the liquid supporting medium having a lower melting temperature and higher specific gravity than foamable metal mixture prepared in accordance with this invention. The liquid supporting medium 34 and the mold half 31 may be maintained at the molten temperature of the metal to be foamed before the foamable metal mixture is poured into the mold half 31 or it may be heated to a temperature lower than the molten temperature of the metal to be foamed. However, the temperature of the mold half '31 should be at least as high as the melting temperature of the substance used for the liquid supporting medium 34. Mold half 31 and liquid supporting medium 34 may be maintained at the preferred temperature either by virtue of the balanced thermal conductivity properties of the mold material, or by an external heating means which for simplicity is not shown. Mold half 32 may be supplied with a quenching medium 39 through tubular member 38, such as oil, water, cooling salt or other cooling medium; the quenching medium may be preferably kept at room temperature. The quenching medium may be agitated by means of an impeller 36 and stored in a storage vessel 40. The quenching medium is circulated through tubular member 38 from vessel 40 to mold half 32 by means of pump 41.

The molten foamable mixture 37 may be poured into mold half 31 on top liquid supporting medium 34 by means of the mixing vessel 4 of FIGURE 1 or the furnace or storage tank 20 of FIGURE 3. For simplicitys sake, these means are not shown in FIGURE 4. After a few seconds, the foamable mixture begins to foam on top of the liquid supporting medium 34. When a smooth nonporous skin begins to form on the regions of the molten metal in contact with the liquid supporting medium 34, mold half 32 may be pulled over mold half '31 so as to provide a quick cooling or quenching of the molten metal foam. Upon cooling, the result-ant product may be taken out of the mold 30 and a foamed rigid metal panel similar to that shown in FIGURE 2 may be formed. The outer portions of the foamed metal that contact the liquid supporting medium form an even, smooth, thin non-porous skin; while the outer portions which do not contact the liquid form a non-even, rough skin. The other regions of the foamed metal that are not in contact with the liquid supporting medium have a uniform even cellular structure due to the uniform and even heat conductivity properties of the liquid supporting medium 34 in the mold half 31. Additionally the molten metal foam need not be q enched but it may be cooled slowly at room temperature.

The mixing of the gas forming agent with the molten metal may be carried out at a temperature lower than the temperature of rapid decomposition of the gas forming agent, in which case the temperature may 'be raised or the pressure in the system lowered to bring about gas release and the resultant foaming. Alternatively, the mixing of the molten metal at the temperature at which rapid decomposition or volatilization of the gas forming agent takes place. The resultant molten metal foam may be then quickly cooled or quenched before the foam is dissipated, producing a solid metal foam of the closed cell type.

It is important that the foaming agent and the metal to be foamed be thoroughly mixed before foaming takes place in order to form a uniform dispersion of gas filled cells within the metal upon foaming. Whether the foaming agent is in the form of a solid, gas, or liquid, it is important that foaming agent be dispersed throughout the molten metal mass before forming occurs. Mixing may be carried out by any of the conventional methods of mixing such as by vibrating, grinding, agitating or any other conventional method. The mixing of the foaming agent with the molten metal may be carried out at the molten temperature of the metal or may be carried out by supplying the foaming agent as a liquid or gaseous stream into the metal to be foamed. Mixing may also be carried out at a temperature lower than the molten temperature of the metal to be foamed; in which case the temperature is raised or the pressure in the system lowered to bring about gas release and the resultant foaming.

It is desirable that the gas forming substance disassociate or volatilize at temperatures slightly above the melting point of the metal to be foamed so that the foam may be readily solidified before it becomes dissipated. This dissipation of the metal foam may be prevented by the use of the liquid supporting medium which provides an even transfer of heat out of the mold so as to readily solidify the metal foam.

The amount of foaming agent used to produce the foam may be varied widely according to the amount of foaming and the density of the foamed product desired. In all cases it is essential that the amount of gas produced by the foaming agent exceed the amount necessary to saturate the molten metal so that closed gas filled cells having a maximum dimension of .002 to 1 inch are formed in the matrix of the metal. In order for the metal to have the desirable properties of :low density coupled with high rigidity the cells in the center layer should have a maximum dimension of between .002 and one inch. Partieular satisfactory high strength low density foamed metal articles have been obtained using as much as 5- 15% of the foaming agent based on the weight of the metal used in the mixture. However foamed articles of this invention may be obtained with as little as .00l% by weight of foaming agent. Use of above 15% of the foaming agent is generally not practical.

The foaming agent may be mixed with an inert diluent such as a gas, alloy, metal or high melting inorganic substance which will prevent rapid decomposition of the foaming until the desired working conditions are obtained, i.e., when the mixture reaches the molten temperature of the metal to be foamed. Thus if sodium bicarbonate is to be effective as a foaming agent for an alloy of zinc and 20% magnesium it must be first thoroughly mixed with 75% to 98% of a relatively inert diluent such as aluminum powder, zinc powder or magnesium powder in order to prevent the bicarbonate from decomposing before it reaches the molten temperature of the zincmagnesium alloy.

This invention is not restricted to any particular metals. Its use is contemplated for relatively low melting metals, such as aluminum, magnesium, zinc and lead and alloys thereof and for high melting metals. In the case of lower melting metals, we prefer to use as foaming agents, particularly, the metal hydrides, such as titanium and zirconium hydride, and also lithium, lithium aluminum, and magnesium hydride, lithium hydride having the advantage that it can be handled in melted form without decomposing, and magnesium hydride having the advantage of leaving a light metal residue after decomposition. Zirconium and titanium hydrides are particularly suitable for use with aluminum, due to their high decomposition temperatures.

Other materials whioh may be used for causing gas formation in foaming metals are sodium carbonate, magnesium carbonate, sodium bicarbonate, calcium carbonate, calcium bicarbonate, potassium chlorate, magnesium bicarbonate, aluminum sulfate, sodium nitrate, zinc sulfate, barium hydroxide, stable hydrates such as chromium oxide hydrate and decomposable organic materials such as copper phthalocyanin, polymethyl siloxane, o-tolyl phosphate, alizarin, tetraphenyl methane, chrysen, picene, oxanide, lmethyl uric acid, sodium benzene sulfon-ate, and ind-anthrene. Gas forming substances other than those mentioned above may be used as the foaming agent in this invention, the preferred ones being those which readily form uniform dispersions with the metal to be foamed and which decompose at normal atmospheric pressure at temperatures not more than a few degrees above the melting or solidus temperature of the metal to be foamed. Hence the choice of a proper foaming agent whether liquid, solid or gas will depend upon the particular metal or alloy that is to be foamed.

The liquid supporting medium of this invention may comprise any salt, combinations of salts, metal, or alloys that melt 'below the molten temperature of the metal tc be foamed and has a higher specific gravity than foamable mixture that is poured on top of this liquid medium to prevent the foamable mixture from sinking into the liquid medium. The foamable mixture has a lower specific gravity (usually about 10-40% lower) than the metal from which it is prepared. This is due to the small production of gas in this mixture. Suitable salts may include: magnesium chloride, lead sulfate, barium sulfate magnesium chlorate, lead borate, sodium metaborate. sodium tetraborate, sodium bromate, sodium bromide. sodium chromate, sodium chloride, silver chloride, potassium pyrosulfide, potassium molybdate, potassium chloride, lead chromate, lead fluoride, lead oxychloride, leaC selenide, lead silicate, lead sulfate and lead chloride Almost any salt or any metal may be chosen as the liquic' supporting medium of this invention, provided that the substance chosen melts below the melting temperature 01 the metal to be foamed, and has a higher specific gravity ban the foamable mixture; for example, lead may be used .s the liquid supporting medium in manufacturing foamed tluminum.

The invention is further illustrated by the following :xamples which illustrate certain embodiments but are lot to be taken as limiting the invention only to those )articular embodiments illustrated, it being understood hat other embodiments and equivalents will be apparent those skilled in the art.

Example 1 90% of an alloy composed of 33% magnesium and i7% aluminum (melting point 361 C.) is intermixed vy intense mechanical agitation, with 10% of zirconium rydride, at a temperature of 465 C. This composition, liquid, is then injected into a stream of molten alumirum metal in a ratio of 1 part of mixture to 9 parts of luminum, and agitated with a rotary high speed agitator or rapid commingling and good dispersion of the hydride n the combined metal streams. The metal is then within .bout 30 seconds, and substantially before foaming has lad time to commence, poured into the mold of FIG- JRE 1. The mold is heated to 550 C. and kept under 1 pressure of 3 atmospheres. A pool of 1 inch in thick- I688 of molten lead covers the bottom portion of said mold. After the molten foamable aluminum is poured nto the mold, the pressure is released and the molten mixture is allowed to foam. The mold is then cooled 0 room temperature.

The resultant article which is removed from the mold [as a weight of about 3.4 kilos and an apparent specific gravity of approximately .4. The resultant article has firm smooth outer skin on the side that contacted the nolten lead of approximately 2 mm. thick, followed by zone of 3 mm. where limited foaming has taken place. ."he side that did not contact the molten lead has a thin ough skin having a varying thickness of between 1 mm. o 4 mm., while the rest of the article is filled with a metal foam throughout.

Example 2 Titanium hydride powder (1 part) is mixed with 12 arts of aluminum powder and the mixture is enclosed in thin walled closely fitting aluminum container. Molten luminum (200 parts) is placed in a cylindrical mixing 'essel and stirred violently by means of an agitator. Vith the aluminum at a temperature of about 675 C. 0 680 C. the container containing the powder mixture 5 tossed or dumped into the molten aluminum and agitaion is continued for an additional to seconds. ifter this time, the agitation is stopped and the mixture 5 then within about seconds poured into the mold of "IGURE 1, the mold being heated to 592 C. and held Lt atmospheric pressure. The bottom of the mold is ined with a two inch deep liquid pool of barium nitrate, he mold and the pool being heated to 550 C. After .11 of the foamable mixture has been poured in the mold, he mixture foams and forms an object conforming to the hape of the mold. The foamed product has a continuous elatively non-porous, smooth surace skin at the outer lortions that were in contact with the liquid pool, while he outer portions that did not contact the liquid pool ras a rough uneven non-porous skin. The rest of the vrticle consists of a uniform low density metal foam.

Example 3 Into an aluminum tube having an outside diameter tf about 1.5 cm. and an inside diameter of about 1.3 cm., here is placed a mixture of .1 kilogram of zirconium .ydride powder with 1.2 kilograms of very finely divided luminum powder, the powder mixture being poured into series of 3 meter lengths of tubing from one end of ash and the tubes being then swaged together, end to nd, to form a much longer tube. Molten aluminum is hen caused to flow into a mixing vessel fitted with an npeller, at a rate of about 1 kilogram per minute and the tubing is introduced into the violently stirred aluminum, where it is melted away. The powder mixture is dispersed into the violently stirred aluminum at a rate of about 15 to .8 meters per minute. The mixture, thus obtained, is allowed before foaming has commenced, to flow over the lip of the mixing vessel into a mold heated at 500 C. and maintained at a pressure of 2 atmospheres. The mold is made by bonding thin layers of sand with a suitable resin around a pattern. The bottom of the mold is filled with a two inch thick pool of liquid bismuth bromide. When the mixture is completely poured into the mold, the pressure is released. The mixture then foams in the mold to provide a foamed article with a smooth, substantially non-porous skin formed at the outside portions of the molten mixture which contact the molten pOOl while the other outside portions have a relatively unsmooth, uneven, non-porous skin.

Example 4 800 grams of zinc are placed in a pressed steel crucible and heated 950 C. 200 grams of nickel are then added and allowed to dissolve. The alloy is stirred well and then 3.38 grams of zirconium hydride suspended in zinc powder are added and stirred therein using an iron rod. The mixture is immediately poured before foaming has had time to take place into the mold half of FIGURE 4 containing a pool of molten mercurous fluoride, the mold and the mercurous fluoride being heated to 900 C. The molten mixture is poured directly on top of the mercurous fluoride solution. After a few seconds the second mold half is placed upon the first mold half to apply a quick quench to the material, the second mold half being filled with water at room temperature. Upon oooling, a foamed object is produced having a tin non-porous outer skin in the outer region of the metal foam that contacts the molten mercurous fluoride salt. The outer regions of the metal foam that do not contact the salt have a rough uneven non-porous skin.

While reference has been made in the above examples to certain specific metals and conditions, other metals and conditions may also be employed. This is true since the principle of foaming in continuous or batch process by the use of the decomposition or volatilization of a solid or liquid gas-forming substance, capable of relatively slow and controllable gas release, in conjunction with a mechanical manufacturing cycle adapted to utilize these controllable properties for continuous or bath foaming can be adapted to any metal systems. For example, the ferrous metals and alloys, cobalt, nickel, copper, titanium, zirconium, niobium, and also the low melting metals such as magnesium, zinc, lithium, aluminum and lead lend themselves to these processes. Foaming may also be produced by introducing a gas under pressure such as hydrogen, oxygen, nitrogen and carbon dioxide instead of a solid or liquid gas-forming agent into the molten metal as shown in FIGURE 12 of the application of Fiedler, Serial No. 751,328. The amount of gas utilized for foaming depends on the metal used, the density of the desired foam and the particular gas used.

While certain modifications and embodiments of the invention have been described, it is of course to be understood that there are a great number of variations which will suggest themselves to anyone familiar with the sub ject matter thereof and it is to be distinctly understood that this invention should not be limited except by such limitations as are clearly imposed in the appended claims.

I claim:

1. The process of making an article comprising metal foam having a specific gravity of less than 1 and having completely enclosed cells distributed therethrough of maximum dimension from .002 inch to 1 inch and having a smooth solid non-cellular layer of material on at least one of its surfaces comprising providing a molten foaimable mixture of metal and a substance which when heated provides a gas which acts to provide closed cells in said metal, providing a mold having disposed on its bottom portion a liquid layer, introducing said molten mixture while substantially unfoamed into said mold directly on top of the liquid layer, foaming said molten mixture in said mold substantially after the introduction of said molten mixture into said mold and while said mixture is in contact with said liquid, said liquid being one which melts below the molten temperature of the metal to be foamed, has a higher specific gravity than the metal to be foamed, does not react deleteriously with the metal to be foamed, and does not substantially dissolve any portion of the metal to be foamed said liquid layer having an upper surface, said upper surface providing a mold surface against which the lower surface of the foamed metal body is formed, said liquid layer and said foamed material being nonadherent, said liquid layer remaining liquid after said foaming is completed, said foamed body characterized by a smooth solid non-cellular layer of the metal of the foaming mixture being formed in contact with said liquid layer.

2. The process of making a metal foam article having a specific gravity of less than 1 and having completely enclosed cells distributed therethrough of maxi-mum dimension from .002 inch to 1 inch and having on at least one of its surfaces a smooth solid non-cellular layer of material, comprising providing a molten foamable mixture of metal and a substance which when heated provides a gas which acts to provide closed cells within said metal, said molten foamable mixture being maintained at the molten temperature of said metal, providing a mold having disposed on its bottom portion a liquid layer, said mold and said liquid layer being heated to the molten temperature of said metal, introducing said molten mixture while substantially unfoamed into said mold directly on top of the liquid layer, foaming said molten mixture by means of gas produced by said substance in said mold substantially after the introduction of said molten mixture into said mold and while said mixture is in contact with said liquid, cooling said molten mixture to a solid so as to entrain said gas in the form of cells within the matrix of the metal, said liquid being one which melts below the molten temperature of the metal to be foamed, has a higher specific gravity than the metal to be foamed, does not react deleteriously with the metal to be foamed, and does not substantially dissolve any portion of the metal to be foamed said liquid layer having an upper surface, said upper surface providing a mold surface against which the lower surface of the foamed metal body is formed, said liquid layer and said foamed material being nonadherent, said liquid layer remaining liquid after said foaming is completed, said foamed body characterized by a smooth solid non-cellular layer of the metal of the foaming mixture being formed in contact with said liquid layer.

3. The process of making a metal foam article having a specific gravity of less than 1 and having completely enclosed cells distributed therethrough of maximum dimension from .002 inch to 1 inch and having on at least one of its surfaces a smooth, even, solid non-cellular layer of material, comprising providing a molten foamable mixture of metal and a substance which when heated produces a gas which acts to provide closed cells in said metal, providing a mold having disposed on its bottom portion -a liquid layer, said liquid layer being composed of a substance which melts at a lower temperature than said metal and does not react with said metal, introducing said molten mixture while substantially unfoamed into said mold directly on top of the liquid layer, foaming said molten mixture in said mold by means of the gas produced by said gas producing substance substantially after the introduction of said molten mixture into said mold and while said mixture is in contact with said liquid layer, cooling said molten mixture to a solid so as to entrain said gas in the form of cells within the mixture, said liquid being one which melts below the molten temperature of the metal to be foamed, has a higher specific gravity than the metal to be foamed, does not react deleteriously with the metal to be foamed, and does not substantially dissolve any portion of the metal to be foamed said liq uid layer having an upper surface, said upper surface pro viding a mold surface against which the lower surfact of the foamed metal body is formed, said liquid layer and said foamed material being nonadherent, said liqui layer remaining liquid after said foaming is completed said foamed body characterized by a smooth solid non cellular layer of the metal of the foaming mixture being formed in contact with said liquid layer.

4. The process of making a metal foam article having a specific gravity of less than 1 and having completely enclosed cells distributed therethrough of maximum di mension from .002 inch to 1 inch and having on at leas one of its surfaces a smooth solid non-cellular layer of material, comprising providing a molten foamable mix ture of metal and a compound which when heated pro vides a gas which acts to provide closed cells in saic metal, providing a mold having disposed on its botton portion a liquid layer, said liquid being composed of z substance which melts at a lower temperature than saic metal and does not react with said metal, heating saiC mold to the melting temperature of said substance, in trodu cing said molten mixture while substantially un foamed into said heated mold directly on top of said liq uid layer so that a portion of said molten mixture contact: said liquid layer, foaming said molten metal mixture by means of the gas produced by said gas producing sub stance in said mold substantially after the introduction 0: said molten mixture into said mold, forming said smooth solid, non-cellular layer of metal on the portions of S8l foamed molten mixture which contact the liquid layer cooling said molten mixture to a solid so as to entraii the gas in the form of cells within the metal matrix, sait liquid being one which melts below the molten tempera ture of the metal to be foamed, has a higher specifi gravity than the metal to be foamed, does not react dele teriously with the metal to be foamed, and does not sub stantially dissolve any portion of the metal to be foame said liquid layer having an upper surface, said upper sur face providing a mold surface against which the lowe surface of the foamed metal body is formed, said liquit layer and said foamed material being nonadherent, sai liquid layer remaining liquid after said foaming is com pleted, said foamed body characterized by a smooth soli non-cellular layer of the metal of the foaming mixture be ing formed in contact with said liquid layer.

5. The process of making a metal foam article havin; a specific gravity of less than 1 and having completely en closed cells distributed therethrough of maximum dimen sion from .002 inch to 1 inch and having on at least oni of its surfaces a smooth, even, solid, non-cellular laye of material, comprising providing a molten foamable mix ture of metal and a compound which when heated pro vides a gas which acts to provide closed cells in sait metal, providing a mold having disposed on its bottom liquid layer, said liquid being composed of a substanci which melts at a lower temperature than said metal ant does not react with said metal, heating said mold to th melting temperature of said substance, introducing sair molten mixture while substantially unfoamed into sai mold directly on top of the liquid layer, foaming sait molten mixture in said mold substantially after the in troduction of said molten mixture into said mold, sait liquid being one which melts below the molten tempera ture of the metal to be foamed, has a higher specific grav ity than the metal to be foamed, does not react deleteri ously with the metal to be foamed, and does not sub stantially dissolve any portion of the metal to be foamet said liquid layer having an upper surface, said upper sur face providing a mold surface against which the lowe surface of the foamed metal body is formed, said liquit layer and said foamed material being nonadherent, saii liquid layer remaining liquid after said foaming is com leted, said foamed body characterized by a smooth solid oncellular layer of the metal of the foaming mixture eing formed in contact with said liquid layer.

6. The process of making a metal foam article having specific gravity of less than 1 and having completely n-closed cells distributed therethrough of maximum diiension from .002 inch to 1 inch and having on at least ne of its surfaces a smooth, even, solid non-cellular layr of material, comprising providing a molten foamable iixture of metal and a compound which when heated at tmospheric pressure provides a gas which acts to proide closed cells in said metal, providing a mold heated to 1e temperature at which said compound decomposes at tomspheric pressure, maintaining said mold at a presure sufficient to prevent decomposition of said comound at that temperature, said mold having disposed on s bottom portion a liquid layer, said liquid layer being omposed of a substance which melts at a lower temperaire than said metal and does not react with said metal, itroducing said molten mixture while substantially unoamed into said mold directly on top of said liquid layer that a portion of said liquid layer contacts the aid molten mixture, releasing the pressure within iid mold substantially after the introduction of all f the molten mixture so as to provide a gas which will foam said molten metal, forming said solid non-cellular layer of metal on the portions of molten mixture which contact the liquid layer, said liquid being one which melts below the molten temperature of the metal to be foamed, has a higher specific gravity than the metal to be foamed, does not react delete'riously with the metal to be foamed, and does not substantially dissolve any portion of the metal to be foamed said liquid layer having an upper surface, said upper surface providing a mold surface against which the lower surface of the foamed metal body is formed, said liquid layer and said foamed material being nonadherent, said liquid layer remaining liquid after said foaming is completed, said foamed body characterized by a smooth solid non-cellular layer of the metal of the foaming mixture being formed in contact with said liquid layer.

References Cited by the Examiner UNITED STATES PATENTS 3,182,363 5/1965 Ferree 22215 .T. SPENCER OVERHOLSER, Primary Examiner; V. K. RISING, Assistant Examiner. 

1. THE PROCESS OF MAKING AN ARTICLE COMPRISING METAL FOAM HAVING A SPECIFIC GRAVITY OF LESS THAN 1 AND HAVING COMPLETELY ENCLOSED CELLS DISTRIBUTED THERETHROUGH OF MAXIMUM DIMENSION FROM .002 INCH TO 1 INCH AND HAVING A SMOOTH SOLID NON-CELLULAR LAYER OF MATERIAL ON AT LEAST ONE OF ITS SURFACES COMPRISING PROVIDING A MOLTEN FOAMABLE MIXTURE OF METAL AND A SUBSTANCE WHICH WHEN HEATED PROVIDES A GAS WHICH ACTS TO PROVIDE CLOSED CELLS IN SAID METAL, PROVIDING A MOLD HAVING DISPOSED ON ITS BOTTOM PORTION A LIQUID LAYER, INTRODUCING SAID MOLTEN MIXTURE WHILE SUBSTANTIALLY UNFOAMED INTO SAID MOLD DIRECTLY ON TOP OF THE LIQUID LAYER, FOAMING SAID MOLTEN MIXTURE IN SAID MOLD SUBSTANTIALLY AFTER THE INTRODUCTION OF SAID MOLTEN MIXTURE INTO SAID MOLD AND WHILE SAID MIXTURE IS IN CONTACT WITH SAID LIQUID, SAID LIQUID BEING ONE WHICH MELTS BELOW THE MOLTEN TEMPERATURE OF THE METAL TO BE FOAMED, HAS A HIGHER SPECIFIC GRAVITY THAN THE METAL TO BE FOAMED, DOES NOT REACT DELETERIOUSLY WITH THE METAL TO BE FOAMED, AND DOES NOT SUBSTANTIALLY DISSOLVE ANY PORTION OF THE METAL TO BE FOAMED SAID LIQUID LAYER HAVING AN UPPER SURFACE, SAID UPPER SURFACE PROVIDING A MOLD SURFACE AGAINST WHICH THE LOWER SURFACE OF THE FOAMED METAL BODY IS FORMED, SAID LIQUID LAYER AND SAID FOAMED MATERIAL BEING NONADHERENT, SAID LIQUID LAYER REMAINING LIQUID AFTER SAID FOAMING IS COMPLETED, SAID FOAMED BODY CHARACTERIZED BY A SMOOTH SOLID NON-CELLULAR LAYER OF THE METAL OF THE FOAMING MIXTURE BEING FORMED IN CONTACT WITH SAID LIQUID LAYER. 